| 摘要 |
PURPOSE:To prevent the illegal listening of a sound signal by transmitting a sound-multiplexed signal obtained by superimposing a noise signal to a main signal and arranging a monaural sound signal to a sub-signal together with scrambling information. CONSTITUTION:An input video signal is modulated to a video carrier by a video modulator 29 and a timing pulse corresponding to the position of a synchronizing signal for the video signal is formed by a timing pulse generator 30. The position of the video carrier which corresponds to the synchronizing signal is level-compressed by a variable gain amplifier 31 based upon the timing pulse. On the other hand, the center frequency 2fH output FM modulation of the sound signal is executed by a sound scrambling modulator 33, the modulated signal is added to a sine wave signal of 1kHz and the multiplexed sound signal is converted into an FM signal by an FM modulator 34 as to audio carrier. The video carrier and the audio carrier are mixed with each other by a mixer 36 and the mixed signal is sent together with service information outputted from a microprocessor 40 through a combiner 38. The receiving side detects the main signal and the sub-signal and outputs only the sub-signal based upon scrambling information. |
